The mechanism of action of the following enzymes will be studied. 1. Coenzyme B12 enzymes. Evidence for radical intermediates has been obtained from ESR spectroscopy. We will now identify the nature of these radicals with compounds containing appropriate isotopes. Experiments will also be done to obtain evidence for the intermediate occurrence of the previously proposed cobalamin-substrate adduct. Nonenzymic studies on the mechanism of C-Co bond cleavage as well as on the reactivity of 2o cobalamins will be made. 2. Amine oxidase (Cu- pyridoxal (?) and flavoprotein). We will definitely identify the structure of the prosthetic group, which is believed to be related to pyridoxal, and determine how the prosthetic group participates in the oxidative process. Studies on flavin-amine oxidase will be concerned largely with the elucidation of the mechanism of action of flavins. Both types of amine oxidases are inhibited by acetylenic amines. This reaction will be studied in detail. This will help identify the prosthetic group in plasma amine oxidase and will clarify the way in which the substrate reacts with flavin in the other type of amine oxidase. Other highly specific active site directed inhibitors will be designed and tested in vivo. 3. Proline racemase. We will try to obtain experimental confirmation for our hypothesis that two SH groups, located on the same subunit, function as proton donor and acceptor during the catalytic process. The presence of Zn plus plus in the enzyme will be confirmed and its role elucidated.